Determining the weight and other dynamic properties of railcars is useful, particularly in railroad distribution yards in which railcars are reallocated based on their weight classifications and must be coupled to each other at controlled speeds.
Railroad distribution yards are used to hold railcars awaiting departure and to align the railcars into trains designated for various destinations. The railcar alignment may be based on the destination of the load of the railcar, the necessity for additional railcars on a specific train, the weight capacity of a train's engine, etc. Generally, railcars are classified into one of four weight categories: light, medium, heavy and extra heavy.
The normal operation at a distribution yard includes the use of a "hump track" which, as the name suggests, is a track which runs over a hump, or hill. A railcar is usually backed up the hump and allowed to free roll down the other side on the hump track. The hump track leads to as many as ninety different tracks, called holding or pullout tracks, to which the railcar may be directed. The different tracks are used for the alignment of the railcars into trains designated for certain destinations. For example, track one could be used to couple railcars destined for Chicago, track two for Philadelphia, track three for New York, etc.
In order to control the railcar dispersement at the distribution yard, each of the railcars should be classified. The process of railcar classification usually requires the ability to determine railcar characteristics, such as speed and weight. The proper coupling of the railcars at speeds that will not damage the railcars or their contents is achieved by predicting the rolling behavior of the railcars.
Therefore, it is necessary to utilize both weight and speed measurements to determine if and how much the railcar should be slowed during its free roll down the hump track. There are usually only a few sections of a hump track which contain braking systems, called retarders. The retarders are used to control the speed of the railcar and prevent coupling at excess speeds which could cause damage. Information regarding the weight and speed of the railcar moving down the hump track must therefore be analyzed quickly and accurately and transmitted to the retarder controller in sufficient time to assess the need for and duration of the operation of the track's braking system.
In determining the necessity for reducing the speed of the moving railcar, the retarder control system analyzes the kinetic energy of the railcar according to the following formula: EQU E=1/2 mv.sup.2
Thus, both the weight of the railcar and its speed must be determined precisely. With the calculation of the energy, the reduction in speed necessary to safely couple the railcar with the next railcar on the designated track may be determined.
Currently, distribution yards utilize micro-switch type "slotted" weight rails to weigh railcars. These weight rails contain slots which have been cut into a section of the rails so that the rails flex as railcars pass over them. The amount of flex trips one or more microswitches. The closing (tripping) of the microswitches sends a signal to a computer indicating the weight class (light, medium, heavy or extra heavy) of the railcar. For example, if only one microswitch closes, the railcar is "light," two indicates "medium," etc.
The micro-switch based "slotted" weight rails have many problems associated with installation, accuracy and cost. Because they are based on mechanical flex of the rail, the continuous stressing of the slotted rails usually results in cracking. Failure generally occurs within three months to two years of use. Breakage of the weight rail disrupts the operation of the distribution yard, is dangerous and may result in derailments. Furthermore, it results in shutting down the distribution yard operation until the weight rail can be replaced.
Additionally, the accuracy of the weight rail system is less than ideal. It is difficult to maintain and adjust the weight classification readings. The undersection of the rail is susceptible to changes resulting from ballast movement caused by vibrations. Therefore, the undersection must be kept properly tamped to get consistent readings. Lastly, the weight rail system only classifies the railcars into one of the four weight categories; thus, the weight of the railcars is only determined within about 25,000 pounds. Greater accuracy is needed for improved control of car coupling.
Finally, the average cost of a micro-switch slotted weight rail is about $30,000 for the rail alone. Additional expense is incurred for installation and for system shutdown upon breakage of a weight rail.
While the weight rails are the most commonly used weighing devices in railroad distribution yards, the use of strain gauges for weighing railcars has also been known in the prior art. Strain gauges are used by a number of companies in the railway industry, including Salient Systems, Siemens, Weightronics, and Revere Technologies, to analyze weight of railcars. Strain gauge systems for use in weighing moving railcars have also been disclosed in U.S. Pat. No. 4,416,342, issued to Snead, and U.S. Pat. No. 4,834,199, issued to Bolland. Like the strain gauges utilized by the railway companies listed above, the strain gauge systems described in the Snead and Bolland references calculate weight based solely on the peak voltage of the signals read from the strain gauges. There is no accommodation for fluctuating baseline voltage levels resulting from the effects of temperature variations or lateral stresses on the strain gauges. Furthermore, the references do not describe any means for reducing or eliminating the debounce effects that the moving railcars often have on the strain gauge readings. In general, debounce effects result in a false peak in the strain gauge signal close in time to the actual peak caused by the weight of the moving railcar exerting direct force on the strain gauge. This false peak may result from vibrations on the railroad track caused by a moving railcar, or other external forces. Whatever the cause, the debounce effect could result in inaccurate weight measurements by a weight system utilizing strain gauges. The prior art strain gauge devices, therefore, must function differently than the present invention or must be installed with a different mechanical system to negate the lateral forces. Otherwise, they will lack much needed accuracy in their weight measurements.